Californian neuroscientists Nicholas Bellono, Duncan Leitch and David Julius have identified the ionic basis for electroreception in sharks and their relatives, skates.
It has been known for decades that sharks, rays and skates use electroreception to interact with and sense their environment. The electroreceptive cells pick up on small voltage fluctuations and relay this information to the central nervous system of the animal. However, the different species have evolved to utilize electroreception for different purposes: sharks use electroreception for hunting, whereas skates are thought to use it for communication.
Published in the journal Nature, the scientists compared the ion channels present in the electrosensory cells of chain catsharks and little skates, which sit in specialised organs called ampullae, and reveal that slight differences in ion channel expression facilitate the distinct roles of the cells in the animals.
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Electrophysiological insight into fish neurons
The team performed an in-depth electrophysiological characterisation of the ion channels present in the electrosensory cells. They were able to investigate the interplay between inward calcium currents and outward potassium currents to understand how the neurons respond to the small changes in voltage they pick up through the salt water.
|Electrosensory Cell Properties||Shark||Skate|
|Resting Membrane Potential||-66mV||-54mV|
|Ion Channel Coupling||CaV1.3 and KV1.3||CaV1.3|
They found differences in the expression of ion channels in these cells between sharks and skates, such that sharks didn’t express large conductance (BK) potassium channels, like skate, but instead made use of large voltage-gated potassium channels that enabled the cells to maintain long-lasting electrical activity, important when tracking prey through the ocean.
Diving deeper into synaptic structure
They also found that at the structural level the synapses of the shark and skate neurons were similar in shape, seen as long ribbons under the electron microscope. However, the shark synapses had many more vesicles in the synapses. This could mean the synapses could maintain the synaptic communication with the central nervous system in response to long-lasting activity in the electrosensory cells. Again, an adaptation that would facilitate tracking of prey and predation.
The paper is a great example of an electrophysiological study that has revealed the underpinnings of a sense that has evolved through time, and underlies the importance of ion channels in biology.
This increased understanding of electrosensation in sharks and skates could perhaps pave the way to development of smart fishing nets or wetsuits that could prevent fishing of sharks and skates, and also better protect surfers.